In the case of textile machines, for example weaving or knitting machines, the thread to be processed must be supplied as continuously as possible, i.e. without interruption, in order to prevent irregularities in the textile goods to be produced. To this end use is made of holding devices for holding the yarn bobbins on which two yarn bobbins are normally mounted whose thread ends are knotted together. If one bobbin is empty, thread is unwound from the next bobbin without interruption. While the thread is being withdrawn from this bobbin, the following bobbin can be mounted and the start of the thread from this bobbin tied with the end of the thread from the bobbin which is presently in use. In such holding devices, there is usually provided a stationary thread eye through which the unwound thread is conducted in order to facilitate unwinding and to maintain a constant thread unwinding force. Moreover, a thread brake can also be provided in front of said thread eye so that the textile machine is supplied with the thread under a tension which is always constant and adjustable. In order to maintain the same amount of tension in the unwound thread prior to and after exchanging the yarn bobbin, the thread eye or the thread brake must always be supplied with the thread from the yarn bobbin in the same respective direction.
Such a holding device is already known from U.S. Pat. No. 3,773,274. This device has a frame part on which a plurality of pairs of bobbin supports are secured. Each pair of bobbin supports is associated with two stationary thread eyes with interposed thread brakes. The bobbin supports are secured to the frame such that the bobbins mounted thereupon are aligned at equal angles with respect to the thread eye associated therewith so that the thread eye is always supplied with the thread from the other bobbin in the same direction after the first bobbin has been emptied. The two bobbin supports of one bobbin support pair can be tipped outwardly in order to be able to substitute a new bobbin for the spent one respectively, while thread is unwound from that bobbin of a pair of bobbins which is not yet empty.
U.S. Pat. No. 2,429,798 discloses another holding device of this type in which two yarn bobbins are secured on a frame in a juxtaposed, inverted position. In the area between the two bobbins a pivotal arm is supported with a thread eye attached at one end. The thread eye is positioned in exact axial alignment with respect to the yarn bobbins in the two end positions of this arm. As soon as the one yarn bobbin is emptied and thread is removed from the other yarn bobbin, the arm pivots from its one end position into the other and thus ensures that the thread eye is respectively positioned in axial alignment of the respective yarn bobbin. While thread is unwound from the new yarn bobbin, the emptied yarn bobbin can be exchanged for a full one.
The two holding devices described above are disadvantageous in that only two yarn bobbins can be stored simultaneously. Thus, immediately after one yarn bobbin has been completely unwound, a new bobbin must be mounted. This results in an undesirable, excessive workload on the operating personnel in the case of small yarn bobbins and/or in the case of large yarn consumption by the textile machine.
The object of the present invention is to provide a holding device of the type stated at the outset in which more than one yarn bobbin can be stored and in which the completely unwound yarn bobbin is exchanged automatically for the next available yarn bobbin.
This object is accomplished in accordance with the instant invention in that a transport device is provided which is driven by an electromotor and on which more than two bobbin supports are mounted and are movable in common such that the respective bobbin to be unwound can be brought into the required association with respect to the stationary thread eye, that a thread scanning device is provided adjacent the unwound thread for detecting the thread as it jumps from the bobbin just emptied to the next bobbin, that this thread scanning device is connected with the electromotor such that, when the thread scanning device responds, the motor moves the transport device to such an extent that the next bobbin is brought into the required association with respect to the stationary thread eye.
In the holding device of this invention, more than two bobbins can be stored simultaneously and are automatically brought in succession to a location in front of the stationary thread eye which is associated therewith. A thread scanning device which is usually located directly adjacent the stationary thread eye responds to the thread when it jumps from the just emptied bobbin to the next bobbin and energizes an electromotor which drives a transport device to which all bobbins are attached and moved in common by said transport device. As soon as the new bobbin has assumed its exactly aligned position in front of the stationary thread eye, the electromotor is de-engerized and the transport device stopped. With the aid of such a holding device it is possible to supply the textile machine with the required yarn supply for a longer period of time, for instance through a whole day, and no operating personnel has to be available any longer after each bobbin change.
In an advantageous further development, the thread segment between two successive bobbins is respectively conducted through at least one clamping member which retains it until it is released when the unwinding thread jumps to the successive bobbin, and the clamping member is secured to a support which is mounted on the transport means approximately parallel to the bobbin axis in a fixed spaced relation from the bobbin support. The clamping member subdivides the free length of the thread segment into two considerably shorter free portions which are substantially insensitive to an air draft. Furthermore, the subdivision of the area to be bridged makes it possible for the operating personnel to better estimate the necessary length of the segment for operation without tension, but not too loose, The spacing of the support, including the clamping member, from the bobbin support on the transport means results in that the change in spacing which occurs at points of curvature or reversal are also subdivided as well, i.e., the spacing from the preceding bobbin to the clamping member and from the clamping member to the subsequent bobbin varies independently of one another by such a small amount that the temporary loosening is confined to magnitudes which are not dangerous. Due to the points of curvature of reversal of the transport means, the clamping member cannot be mounted on a frame disposed on a bobbin support as, for example, the frame of the main support arm which supports the thread eye, since this frame pivots outwardly at the points of reversal and would thus enlarge instead of reduce the area to be bridged by the thread segment, thus producing tension. In view of the low clamping action of the clamping member which is provided, the thread segment would be ripped out of this clamping member altogether and would hang completely free along the rest of the transport path. The clamping member has a clamping effect which is dimensioned to be so slight that the continuous thread supply is not impeded, since the unwinding tension acting on the hitherto resting thread segment without tension while the preceding bobbin is unwound is sufficient to withdraw the thread segment out of the clamping member without a tug. The slight clamping action is completely sufficient for holding the resting segment without tension.
A control element is advantageously disposed on the support to keep its orientation with respect to the bobbin axis constant and to prevent changes of thread direction adjacent the clamping member at the points of curvature and reversal, thus eliminating undesirable tension and/or friction.
In a preferred embodiment, a support arm for the thread eye is secured to the support of the clamping member. An additional mount for the thread eye can thus be omitted. The rigid association between the bobbin support and the support for the clamping member ensures an identical association of the thread eye relative to the bobbin axis.
The constant orientation of the support is ensured advantageously in that the support is disposed to be rotatable about its axis relative to its amount on the transport means and is firmly connected with a control bar mounted on the bobbin support to be rotatable and longitudinally displaceable. The control bar follows the direction of the transport means in the case of rectilinear movement. In the case of curves or points of reversal, it pivots automatically into a position corresponding to the respective arc chord. In this way, the same side of the support remains facing the thread bobbin. The same applies to the clamping member and the support arm. The longitudinal displaceability of the control bar, advantageously accomplished in a simple manner by means of an elongated hole on the control bar, facilitates the adaptation to the direct distance between the support and the bobbin axis which is reduced at the points of curvature and reversal. The thread eye supported by the support arm is advantageously designed as an elongated loop for the same reason.
In a preferred embodiment, a plurality of elastic clamping members are provided. The free areas of the thread segment are reduced advantageously in this way. Moreover, it is possible in this manner to bridge the difference in height between the lower end of the preceding and the thread eye of the successive bobbin instead of by means of a diagonal path of the thread segment or at least one portion of these areas formed by the clamping member. It is also possible to conduct the thread segment at such an angle that it passes along the device elements and across free spacings as short as possible.
A clamping member is favorably located on the support approximately flush with the lower bobbin rim and a clamping member is positioned approximately in the plane of the thread eye so that the thread segment extends from the lower area of the preceding bobbin at first close to the control bar and then approximately perpendicular thereto along the support and finally approximately parallel to the transport means freely to the upper area of the support and then to the thread eye of the successive bobbin.